1. Field
Embodiments described herein relate generally to a switching power supply apparatus.
2. Background Art
Conventionally, the switching power supply apparatus has been widely utilized for a reason of its high power processing efficiency. The switching power supply apparatus is a power supply apparatus including a switching element, a smoothing circuit formed of an inductor and a capacitor, and a feedback control circuit for keeping an output power supply voltage constant. As for its operation, a smoothing circuit smoothes a rectangular wave obtained by connecting a high potential terminal and a low potential terminal of a supply source alternately by means of the switching element, and an output power supply having a voltage, which is different from that of the supply source is obtained. The switching element assumes extremely low resistance when it is in the on-state, whereas the switching element assumes extremely high resistance when it is in the off-state. In both cases, power dissipation in the switching element is very low. In addition, ideally, the inductor and capacitor do not dissipate power in their charging and discharging operation. Therefore, the switching power supply apparatus has a feature that the power dissipation is low.
As for the feedback control circuit in the switching power supply apparatus, either a voltage feedback control mode or a current program mode is mainly used (see, for example, U.S. Patent Application No. 2009/0267582).
The voltage feedback control mode is a voltage feedback pulse-width modulation mode in which a voltage of an output power supply is measured and a time ratio between the on-state and off-state of the switching element is changed according to a difference between the measured voltage and a reference potential. As a matter of fact, however, a significant transfer delay is caused in the smoothing circuit formed of the inductor and capacitor in the operation of the voltage feedback control mode. Therefore, it is difficult to stabilize the control operation.
On the other hand, in the current program mode controls, the peak of inductor current in which a current flowing through an inductor is measured and the switching element is kept in the on-state until the inductor current reaches a certain target value and then the switching element is brought into the off-state. The target value of the inductor current used here is calculated from a difference between a voltage of the output power supply and a reference potential. Its feedback control becomes a double-loop structure and is complicated. However, the delay in the smoothing circuit, which poses a problem in voltage-mode controllers, is significantly reduced in the current program mode. Therefore, it is comparatively easy to stabilize its control operation.
As an important characteristic in the switching power supply apparatus, there is a transitional response characteristic (also known as transient response) which appears in the case where the load current has changed remarkably and rapidly. If the transitional response characteristic is slow, then a phenomenon that the output voltage becomes low in a moment occurs, for example, when a state in which the load current is small has abruptly changed to a state in which the load current is large. Conversely, when a state in which the load current is large has abruptly changed to a state in which the load current is small, the output voltage rises in a moment.
In the voltage feedback control mode, nonlinear control is frequently used. In the nonlinear control, a difference between the output voltage and the preset voltage caused by a change of the load current is detected and the on-time of the switching element is prolonged extremely to cancel the difference. In the current program mode, however, it is difficult to adopt the nonlinear control, therefore the transitional response characteristic obtained when the load current has varied often poses a problem especially in the switching power supply apparatus using the current program mode.
In this way, the switching power supply apparatus using the conventional voltage feedback control mode has a problem that it is difficult to ensure the stability. Furthermore, in the switching power supply apparatus using the conventional voltage feedback control mode, parallel operation is challenging to achieve and it is difficult to shrink the size of the apparatus and reduce the cost of the apparatus. In addition, problems with non-equal current sharing between phases, causing potential component failures is quite common.
On the other hand, in the switching power supply apparatus using the conventional current program mode, which is an improved type for the switching power supply apparatus using the conventional voltage feedback control mode, there is a problem that it is difficult to improve the transitional response characteristic.